Coating composition for pyrophoric metal powders and shavings



United States Patent "ice 3,407,089 COATING COMPOSITION FOR PYROPHORIC METAL POWDERS AND SHAVINGS Charles F. Sampson, Springfield, Howard M. Rue, Media, and George S. Rostron, Springfield, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Filed July 8, 1965, Ser. No. 470,617 1 Claim. (Cl. 117-100) ABSTRACT OF THE DISCLOSURE The pyrophoric nature of finely divided particles of metal such as iron can, for the most part, be overcome by coating the particles with a light naphthenic petroleum oil coating 1 to 3 wt. percent of glycerol monooleate.

This invention relates to the treatment of pyrophoric metals to render them safe for storage and shipment. Particularly, the present invention concerns the coating of finely divided metal powders such as filings and shavings, which may become pyrophoric as a result of rapid oxidation, to render them innocuous.

In the art it is known to coat finely divided particles of metal to control their pyrophoric tendencies. The prior art has employed varnishes, paraffin, bees-wax, and more recently organic nitriles having a carbon-carbon unsaturation.

It is an object of this invention to provide a simple treatment for metal powders and shavings to prevent their oxidation.

It is a further object of this invention to provide a composition for treating pyrophoric metal powders in order to render them safe for storage and shipping.

It is a further object of the present invention to provide for treatment of pyrophoric metals employing a composition produced for relatively inexpensive and readily available materials.

It is a further object of the present invention to provide a method for applying a composition to pyrophoric metals so as to prevent their oxidation.

It has been found that the objects of the present invention are achieved by spraying the pyrophoric metals with a composition of a particular light petroleum fraction and glycerol monooleate.

The need for the present invention arose from the problem of rapid oxidation of metal filings and shavings that were stored prior to foreign shipment and the frequent fires during shipment when the metal powder was stored in the holds of ships. Thus, the means of oxidation prevention had to be commensurate with the rather low cost, large quantity, low quality pyrophoric material. Such materials are the iron, steel, steel alloy, aluminum waste from machining and other fabrication processes.

The instant invention although directed to low quality pyrophoric materials is also suitable for use on high grade materials used for pyrotechnic purposes.

The coating composition is applied to the pyrophoric metal by spraying. Since the metal is usually in a finely divided state such as powder, filings or shavings, it is allowed to fall through a fine mist of the coating composition, or flow down an inclined bed while the coating composition is sprayed on the moving bed at some point. Alternatively, a pile or mound of the metal powder may be sprayed until by sampling, it is determined that the entire mass of material is substantially coated. The latter alternative is no preferred since this method employs far more of the coating composition than actually necessary.

The amount of coating composition needed to achieve the objectives of the present invention, i.e., eliminate the 3,407,089 Patented Oct. 22, 1968 pyrophoric nature of the metal powder, is only that required to wet the surface of the metal particles. The light petroleum fraction found suitable for the objectives of the present invention is a low viscosity, high boiling naphthenic-base material obtained by the vacuum distillation of straight run naphthenic crude that has been caustic treated and has a boiling range of about 550 to 750 F.

In the art this material is known as an untreated transformer stock. As indicated, there has been an initial caustic treatment which removes the naphthenic acids. In order to produce commercial grades of transformer oil, the stock material is subjected to acid and clay treat ment which reduce its tendency towards oxidation, moisture, acids, soap, salts, and suspended matter to a minimum.

About 97 to 99 weight percent of the coating composition is the light, naphthenic petroleum fraction.

Transformer oil, i.e., the highly refined stock described above, is also suitable for the treating process. Of course the transformer oil is more expensive than the untreated transformer stock, which is entirely equivalent in its antipyrophoric effect to the highly refined material for the purposes of the present invention.

The glycerol monooleate added to the naphthenic petroleum oil is the monoester of oleic acid and glycerine. Esterification processes are so well known in the art that further description of the glycerol monooleate is not needed here. The glycerol monooleate is present in the coating composition in the range of from about 1 to 3 weight percent of the total composition.

When glycerol monooleate is added to the light, naphthenic oil in the proportions described, the ingredients are readily miscible, forming a permanent solution. The mixing is achieved by simply adding the glycerol monooleate to the oil at ambient temperature and agitating for a time sufiieient to produce an even distribution of glycerol monooleate throughout the oil.

Example I A coating composition having the desired properties was prepared and tested in the following manner:

Coating composition: Wt. percent Naphthenic petroleum fraction 98 Glycerol monooleate 2 The oil composition above was tested for rust protection in the humidity cabinet according to ASTM Dl748- 62T. In this test 2 by 4 inch panels of steel, which have been coated with the above oil composition according to the method set out in ASTM D-1748-62T, are suspended in the humidity cabinet, which is maintained at 121 F. The panels were tested for hours-to-failure. In order to make this type of evaluation, the coated metal panels were removed from the humidity cabinet once a day and examined for rust spots. The panels passed or failed as indicated in ASTM Dl74862T.

Three panels coated as indicated were run at the same time. All three samples went 888 hours (37 days) to failure. This is considered a significant improvement over a commercially available coating material that has been in extensive use prior to this invention and which failed at 330 hours (14 days) in the same test.

The commercially available coating material was a 3 mixture of the same type of naphthenic petroleum fraction as employed in the present invention with two additives as follows:

Wt. percent Naphthenic petroleum fraction 97.8 Petrosan (methyl ester of lard oil) 0.2 Nalco (imidazolines) 2.0

The imidazolines are not compatible with the naphthenic fraction and must be added to the composition as it is sprayed onto the metal particles.

Any naphthenic oil having a boiling range of 550 to 750 F., viscosity of 55 to 60 SUS at 100 F. and neutralization number of 0.0 is suitable as the petroleum oil portion of the composition. By the term naphthenic is meant oils containing substantial amounts of carbon atoms in naphthenic rings--C (this method of classifying oils is described in Analytical Chemistry, volume 30, 1224 (1958), and Industrial and Engineering Chemistry, volume 48, 2232 (1956)).

The invention claimed is:

1. The process of eliminating the pyrophoric nature of a finely divided metal which comprises coating said metal with a composition comprising a light naphthenic petroleum oil having a boiling point in the range of 550 to 750 F., containing 1 to 3 weight percent of glycerol monooleate, said coating composition being capable of eliminating the pyrophoric nature of said metal.

References Cited UNITED STATES PATENTS 2,623,887 12/1952 Matuzak 106l4 2,900,262 8/1959 Green 106l4 2,564,423 8/1951 Barnum 106-14 2,560,202 7/1951 Zimmer 106-14 3,080,330 3/1963 Rudel 106-14 JULIUS FROME, Primary Examiner. 

